Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS AND METHOD FOR ELECTROCARDIOGRAM-ASSISTED
BLOOD PRESSURE MEASUREMENT
FIELD OF THE INVENTION
The present invention relates to non-invasive automatic blood pressure
measurement in
humans whereby electrocardiogram (ECG) data acquisition is ergonomically
integrated into the
oscillometric blood pressure monitoring paradigm to provide robust evaluation
of blood
pressure and vessel stiffness.
BACKGROUND
Accurate automatic non-invasive assessment of blood pressure employing
oscillometry is a
challenge. Factors like arrhythmias, obesity, and postural changes tend to
obscure arterial
amplitude pulsations that are sensed by the cuff, thus introducing errors in
these
measurements. Therefore, robust and reliable non-invasive estimation of blood
pressure
remains a topic of active research and inquiry.
Various prior art devices and techniques have explored newer methods that not
only
bolster the popular oscillometric technique but also go beyond it for
estimating blood pressure.
For example, the use of an ECG signal, which is a higher fidelity
physiological signal, is proposed
for reconstructing an oscillometric signal contaminated with artifacts to
provide accurate
assessment of blood pressure. Similarly, synchronized ECG signals are employed
for removing
motion artifacts from oscillometric signals to increase the accuracy of blood
pressure
measurements.
Some attempts have been made to combine blood pressure and ECG monitoring in a
single
device by incorporating ECG electrodes in a blood pressure cuff in an effort
to render
compactness to these monitors. The AMON system combines pulse and ECG sensors
in a single
wrist worn enclosure for continuously collecting and evaluating multi-
parameter vital signs. A
US Patent Application proposes a combined ECG and blood pressure monitor
resembling a
wristwatch whereby the whole device is contained inside the wrist enclosure.
Another US
Patent presents a simplified ECG monitoring system in which two ECG electrodes
made of
sintered Ag/AgCI coating are incorporated in a brachial blood pressure cuff
while a third ECG
electrode (made in the same manner) is provided inside a pulse oximeter finger
probe.
A widely researched method that goes beyond oscillometry comprises the
estimation of
blood pressure from pulse transit time or pulse wave velocity - the time taken
by a cardiac
pulse to travel between the heart and a peripheral arterial site or between
two peripheral
arterial sites. Many prior art publications propose the pulse transit time-
blood pressure
correlation analysis method for assessing blood pressure. Here, the inverse
correlation between
pulse transit time and blood pressure is utilized for blood pressure
estimation, whereby a rise in
blood pressure causes the pulse transit time to decrease and vice versa. Other
researchers have
proposed to estimate blood pressure by studying the dependence of pulse
transit time on
applied cuff pressure.
All of the above described techniques and methods show promise towards
increasing the
robustness of automatic non-invasive blood pressure measurement. However, they
have not
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been suitably integrated into one system along with appropriate analysis
algorithms. The
methods that propose to increase accuracy of oscillometric blood pressure
measurement by
analyzing it in the presence of a higher fidelity ECG signal employ obtrusive
gel chest and/or
auxiliary electrodes and do not obtain blood pressure information from the
dependence of
pulse transit time on cuff pressure. The systems that propose integrating ECG
monitoring inside
a blood pressure monitor do not report any analysis algorithms that may be
employed to
increase accuracy of blood pressure measurement. In addition, these systems
employ hard
and/or gel electrodes under cuff, which are ergonomically problematic and may
affect arterial
pulsations sensed by the cuff. The pulse transit time-blood pressure
correlation method is
cumbersome since it requires frequent calibration using another blood pressure
monitor.
Moreover, since blood pressure-pulse transit time correlations are weak, this
method is not
reliable for robust blood pressure estimation. Finally, the approaches that
measure blood
pressure from the dependence of pulse transit time on cuff pressure use a
number of auxiliary
pressure and/or ECG sensors to the cuff rendering them inconvenient and do not
obtain blood
pressure information from the oscillometric signal itself.
SUMMARY OF THE INVENTION
The present invention addresses the above-mentioned limitations in the field
of non-
invasive automatic blood pressure measurement. An ECG-assisted blood pressure
monitoring
device is described wherein high fidelity ECG data acquisition is
ergonomically integrated with
the oscillometric blood pressure monitoring paradigm and a comprehensive
analysis platform is
provided for robust blood pressure and vessel stiffness evaluation. Dry, thin,
and flexible ECG
electrodes are incorporated on the inner surface of a brachial blood pressure
cuff. In addition,
dry and rigid ECG electrodes are provided on the control unit. The control
unit includes
hardware and software for simultaneous ECG and arterial pulse wave or
oscillometric data
acquisition and analysis. During a measurement, the cuff is wrapped around the
upper arm
while electrodes on the control unit are touched with the other hand. All
measurements are
accomplished by inflating the cuff to a pressure above the expected systolic
pressure, and then,
deflating it at a desired constant rate (generally, about 3 mmHg/s) until a
pressure of less than
the expected diastolic pressure is reached. At this point, the residual
pressure inside the cuff is
completely released and the measurement is complete.
In one embodiment of the invention, two flexible ECG electrodes made of
conductive fabric
are stitched on the inner side of a brachial blood pressure cuff which has an
inflatable bladder
inside. One of the conductive fabric electrodes acts as the first ground
electrode while the
other acts as the first sensing electrode for ECG data harvest. Both these
electrodes are dry and
re-usable ECG electrodes. The large surface area of these electrodes and their
soft texture
ensures that they make good and permanent contact with the skin to enable
acquisition of a
high quality ECG signal. Moreover, the softness and flexibility of these ECG
electrodes ensures
that they do not affect the pressure sensing capability and accuracy of the
blood pressure cuff.
Two rigid ECG electrodes, one made of stainless steel and the other made of
high-
impedance rubber, are attached on the device box. The stainless steel
electrode acts as the
second ground electrode while the high-impedance rubber electrode acts as the
second sensing
electrode for ECG data harvest. Again, these are dry and re-usable ECG
electrodes.
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Both the flexible electrode pair inside cuff and the rigid electrode pair on
device box are
designed as active ECG electrodes whereby the respective amplification
circuits are in close
proximity with the electrodes. That is, the ECG signal is amplified at a site
physically very close
to the electrodes and then transmitted further. This reduces the problem of
signal transmission
loss and interference in the signal transmission line. As a result, the
acquired ECG signal is of
high quality with minimum noise.
Moreover, the use of a high-impedance sensing electrode on the device box
reduces the
problem of half-cell potential to allow rapid and good quality ECG data
acquisition. Rapid ECG
data acquisition is an important requirement in an oscillometric blood
pressure monitor. This is
because an oscillometric signal acquired by such a monitor generally has a
duration range of 30-
90 s. Therefore, the response of the ECG system should be fast enough to
enable acquisition of
a good quality analogous ECG signal in the same timeframe.
The two active ECG electrode pairs (two conductive fabric electrodes along
with
amplification circuitry inside cuff, and one high-impedance rubber and one
stainless steel
electrode along with amplification circuitry on device box) are connected to
an electrical
conditioning unit for further amplification and filtering. The acquired ECG
signal is similar to the
one obtained using a lead 1 configuration.
The ECG measuring unit has the capability of injecting a high frequency ("' 20
KHz) and low
magnitude current (- 100 l.LA) into the ECG measuring circuit for checking the
goodness of
contact between the electrodes and the human body. The device generates an
alarm alerting
the user in case the contact between the electrodes and the human body is
found to be weak
or inappropriate.
A motorized pump inflates the cuff while a pressure transducer measures cuff
pressure. A
voltage-controlled pressure release valve guided by ECG R-peak information
accomplishes cuff
deflation during which the monitor acquires analogous arterial pulse wave or
oscillometric
data.
ECG R-peak locations are used for isolating arterial pulses that facilitates
the calculation of
their amplitude. Moreover, ECG R-peak locations and arterial pulses are used
for calculating
pulse transit time.
An oscillometric envelope is constructed by mapping the change in arterial
pulse amplitude
in response to changing cuff pressure. The cuff pressure at which the maximum
of the
oscillometric envelope is reached gives the mean blood pressure. Empirical
coefficients, that is,
certain ratios of the maximum of the oscillometric envelope, are used for
evaluating diastolic
and systolic blood pressure.
Similarly, pulse transit time envelopes are constructed by mapping the change
in pulse
transit time, measured between ECG R-peak and different locations on the
arterial pulse, in
response to changing cuff pressure.
The cuff pressure at which the maximum of the pulse transit time envelope,
calculated
from ECG R-peak and maximum slope of arterial pulse wave, is reached gives the
mean blood
pressure. Empirical coefficients, that is, certain ratios of the maximum of
the pulse transit time
envelope, calculated from ECG R-peak and maximum slope of arterial pulse wave,
are used for
evaluating diastolic and systolic blood pressure.
Additionally, the cuff pressure at which the maximum of the pulse transit time
envelope,
calculated from ECG R-peak and top of arterial pulse wave, is reached gives
the systolic blood
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pressure. Finally, the cuff pressure at which the maximum of the pulse transit
time envelope,
calculated from ECG R-peak and bottom of arterial pulse wave, is reached gives
the diastolic
blood pressure. We note that no empirical coefficients are required for
calculating diastolic and
systolic blood pressure when pulse transit time envelopes are calculated from
ECG R-peak and
top/bottom of arterial pulse wave.
A fusion algorithm is employed for combining the blood pressure information
obtained
from the ECG-assisted oscillometric and pulse transit time-cuff pressure
analyses to provide a
robust and accurate evaluation of blood pressure.
Finally, a regression analysis is carried out between the oscillometric and
pulse transit time
envelopes to provide vessel stiffness parameters.
The device has capability of repeating blood pressure measurements
periodically, for
continuous blood pressure monitoring.
A central processing unit (CPU) runs all software and interacts with various
device
components to simultaneously acquire/analyze ECG and oscillometric data, and
to transmit
information as required. The device has onboard memory to store all
information and a liquid
crystal display, which displays the measured blood pressure values as well as
the ECG and the
arterial pulse waveforms. Moreover, the device has functionality of
transmitting information to
a personal computer and/or a smartphone wirelessly.
The personal computer and smartphone have customized software for storing,
analyzing,
and visualizing physiological information received from the device. This
allows the user to
assess/visualize parameters such as blood pressure trends, arterial stiffness
variations, and
arrhythmia periods in a flexible and adjustable manner.
Once physiological information is stored inside the personal computer and/or
smartphone,
it is transmitted via Internet or cellular network to designated recipients
for medical evaluation
and patient management.
The invention describes a sensing unit, comprising a cuff for measuring blood
pressure, a
first dry flexible sensing electrode positioned between a body part and an
inside surface of the
cuff, for connection to a human body. One or more dry flexible ground
electrodes is positioned
between a body part and an inside surface of the cuff for connection to the
human body and a
second sensing dry electrode is provided for connection to the human body such
that a heart of
the human body is intermediate the first sensing and second sensing
electrodes.
The system further comprises a second dry ground electrode near the second
sensing
electrode, for equalizing static potential on body and reducing noise.
The first and second sensing electrodes are active electrodes to reduce
transmission noise.
Moreover, the first and second sensing electrodes are high impedance
electrodes to reduce
half-cell potential. Further, the system comprises a device box, wherein the
second sensing
electrode is positioned.
The system for non-invasive blood pressure estimation comprises an
electrocardiogram
(ECG) measuring unit, an arterial pulse wave measuring unit in communication
with the ECG
measuring unit, a cuff for measuring blood pressure in communication with the
arterial pulse
wave measuring unit, two or more electrodes connected to the ECG measuring
unit, and an
analysis unit connected to the ECG and arterial pulse wave measuring unit.
The analysis unit comprises an ECG measuring subunit, a cuff pressure and
arterial pulse
wave measuring subunit, a subunit that uses ECG R-peak information for
isolating arterial pulse
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waves, a subunit for measuring pulse transit time between ECG R-peak and
specific points on
the arterial pulse wave and mapping the measured pulse transit time with
corresponding cuff
pressure, obtaining pulse transit time envelopes, a subunit for de-trending
cuff pressure signal
and finding arterial pulse wave amplitude using ECG R-peak information, and
mapping the
5 measured amplitude with corresponding cuff pressure, obtaining an
oscillometric envelope. A
subunit analyzes morphology of pulse transit time envelopes, to obtain pulse
transit time-based
blood pressure estimation. Moreover, a subunit analyzes morphology of the
oscillometric
envelope, to obtain oscillometric blood pressure estimation.
In this system, the ECG measuring unit uses a high frequency, low magnitude
current for
checking the quality of contact between the electrodes and the human body.
Moreover, the ECG measuring unit comprises two or more flexible dry electrodes
attached
to the internal surface of a brachial cuff and two or more dry rigid
electrodes attached to a
device box.
The analysis unit is selected from the group consisting of a software on a
computer,
software on a smartphone, hardware having an Field-Programmable Gate Array
(FPGA)
architecture, hardware having an Application-Specific Integrated Circuit
(ASIC) architecture, and
as a standalone unit having software and hardware therein.
The system has communication means for transmitting physiological information
through a
network to designated recipients for medical evaluation and patient
management.
The system employs ECG R-peaks as one means for isolating arterial pulse
waves.
The sensing unit comprises dry electrodes.
The analysis unit further comprises a subunit for fusing the oscillometric and
pulse transit
time analyses to obtain robust blood pressure estimation.
The system also has a subunit for evaluating vessel stiffness parameters based
on fusing
information obtained from the oscillometric and pulse transit time analyses.
The system employs coefficient-based method for evaluating diastolic and
systolic blood
pressure from oscillometric analysis, comprising steps of: (a) obtaining
oscillometric envelope
by using ECG R-peak information for de-trending the cuff pressure signal and
for isolating
arterial pulse waves; (b) using the maximum of the oscillometric envelope for
determining
mean blood pressure; and (c) using empirical coefficients on the oscillometric
envelope for
evaluating diastolic and systolic blood pressure.
it also employs a coefficient-based method of evaluating diastolic and
systolic blood
pressure from pulse transit time analysis, comprising the steps of: (a)
calculating pulse transit
time between an ECG R-peak and maximum slope on an arterial pulse wave to
obtain pulse
transit time envelope; (b) using the maximum of the pulse transit time
envelope for
determining mean blood pressure; and (c) using empirical coefficients on the
pulse transit time
envelope for evaluating diastolic and systolic blood pressure.
Finally, the system employs a method of evaluating coefficient-free diastolic
and systolic
blood pressure from pulse transit time analysis, comprising the steps of: (a)
calculating pulse
transit time between ECG R-peaks and specific points on arterial pulse waves
to obtain pulse
transit time envelopes; (b) using the maximum of the pulse transit time
envelope that is
obtained by measuring pulse transit time between ECG R-peaks and bottom of
arterial pulse
waves, for evaluating diastolic blood pressure; and (c) using the maximum of
the pulse transit
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time envelope that is obtained by measuring pulse transit time between ECG R-
peaks and top
of arterial pulse waves, for evaluating systolic blood pressure.
The system fuses oscillometric and pulse transit analyses to obtain robust
blood pressure
estimation.
The system has further capability of repeating the evaluation of diastolic and
systolic blood
pressure periodically, for continuous blood pressure monitoring.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention will be disclosed in detail
with reference
to the drawings, in which:
FIG. 1 shows the ECG-assisted blood pressure monitoring device in use on a
human;
FIG. 2 shows the ECG-assisted blood pressure monitoring device;
FIG. 3 shows an operational diagram of the ECG-assisted blood pressure
monitoring device;
FIG. 4 shows a circuit diagram of the flexible electrode amplification unit;
FIGS. 5a through 5d show graphical representations of the coefficient-based
ECG-assisted
oscillometric and the pulse transit time-cuff pressure analyses;
FIGS. 5e and 5f show the oscillometric and pulse transit time envelopes
obtained from the
coefficient-based ECG-assisted oscillometric and the pulse transit time-cuff
pressure analyses;
FIGS. 6a and 6b show a graphical representation of the coefficient-free ECG-
assisted pulse
transit time-cuff pressure analysis;
FIGS. 6c and 6d show pulse transit time envelopes obtained from the
coefficient-free ECG-
assisted pulse transit time-cuff pressure analysis; and
FIG. 7 shows a flowchart depicting the method of estimating systolic,
diastolic, and mean
pressure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be set forth in detail
with reference
to the drawings, in which like reference numerals refer to like elements or
method steps
throughout.
FIG. 1 shows an exemplary system and configuration in which a subject 01 is
being
monitored by the ECG-assisted blood pressure monitoring device 05 supported on
a surface 45.
The brachial blood pressure cuff 15, which is worn by the subject 01 on
his/her left arm, is
connected through an air hose 10 to the device box 05. The active flexible ECG
electrodes (not
shown) in the blood pressure cuff 15 are connected with wires (not shown),
which go through
the air hose 10, to the device box 05. In another implementation, wrist blood
pressure cuff may
be used. The subject 01 touches the active rigid ECG electrode pair 20, 25
attached on the
device box 05 with his/her right hand to complete the ECG circuit. The
start/stop button 40 is
pushed to initiate a recording. Visualization and numerical summary of the
physiological
parameters monitored are displayed on a liquid crystal display 30 provided on
the device box
05. All information is transmitted wirelessly to a personal computer and/or
smartphone via the
antenna 35. In some embodiments, the device is capable and configured to
transmit data
wirelessly using a long distance wireless protocol, such as cellular wireless
standards, such as
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GSM, 3G, 4G, or 5G wireless standards. in some embodiments, the device is
capable and
configured to transmit data wirelessly to communicate with WiFi enabled
devices, such as by
utilizing the IEEE 802.11 standard for wireless communication. In some
embodiments, the
device is capable and configured to transmit data wirelessly with other
devices under a short
range standard, such as the BluetoothTM standard. One skilled in the art would
appreciate that
the right side may be used instead of the left for the brachial cuff, and that
the rigid electrode
pair on the device box should be touched with an opposite limb.
FIG. 2 shows an exemplary close-up of the ECG-assisted blood pressure
monitoring device
05. The inner side of the brachial blood pressure cuff 15 is shown along with
the active flexible
electrode pair 50, 55. In one embodiment these flexible ECG electrodes 50, 55
are rectangular
in shape and are made of medical grade silver plated (92% nylon and 8%
DorlastanTM)
stretchable conductive fabric (0.50 mm thickness and less than 10/Square
surface resistivity).
The area of each of these conductive fabric electrodes (50, 55) is about 75
cmz. One skilled in
the art would appreciate that other electrodes would also perform the
invention, for example a
flexible electrode can be manufactured from a number of rigid electrodes on a
flexible fabric
substrate. The electrodes may be dry, gel, or another formulation known in the
art, however
dry electrodes provide more convenience and less mess. They need not be
disposed of as
medical waste after each use, as is the case with gel electrodes.
The flexible electrodes 50, 55 are stitched on the inner side of the brachial
blood pressure
cuff 15, or may be positioned between the cuff and the arm, so as to be held
by the cuff 15.
Connections to the active flexible electrodes are made using metallic snap
buttons (not shown).
The air hose 10 connects the bladder (not shown) inside the blood pressure
cuff 15 to the
device box 05. Wires (not shown), which go through the air hose 10, connect
the active
conductive fabric electrodes 50 and 55 to the device box 05. In one
embodiment, the active
rigid ECG electrode pair 20, 25, which are circular in shape, are fixed on top
of device box 05.
The area of these ECG electrodes (20 and 25) is about 22 cm2 each while their
thickness is
around 4 mm each. A recording is initiated by pushing the start/stop button
40. The liquid
crystal display 30 displays all relevant information, for example, mean blood
pressure, diastolic
blood pressure, systolic blood pressure, etc. In one embodiment, information
may be
transmitted wirelessly to a personal computer (PC)/smartphone via the antenna
35. In another
embodiment (not shown in the FIG. 2) the processing is done locally in the
local unit and the
information is not transmitted. In yet another embodiment (not shown in the
FIG. 2) the
information is transmitted using a wired link to a personal computer
(PC)/smartphone.
It should be understood that a typical system may include fewer or more
electrodes than
presented in FIGS. 1 and 2, which may be made and placed in a different way.
In preferred
embodiment, the sensing electrodes are active. In another embodiment some or
all sensing
electrodes may be high impedance electrodes. The area of the electrodes and
their material
may be also different than the ones presented in the preferred embodiment.
The preferred embodiment presented in FIGS. 1 and 2 includes one sensing
electrode 50
and one ground electrode 55 under the cuff 15 and one sensing 20 and one
ground electrode
25 on the box 05. In another embodiment, zero, one or more ground electrodes
may be used.
In one embodiment, the electrodes 20, 25 may be placed on the body and not on
the
device box. The placement on the body should be such that the heart is in
between the
electrodes in the cuff 15 and electrodes 20, 25. In another embodiment, all
electrodes can be
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external and not connected to the cuff or to the device box. More than two
sensing electrodes
may be used. In yet another embodiment, external ECG unit with its electrodes
can be
connected to the device box or the computer and can be used to acquire
analogous ECG data
during blood pressure monitoring procedure.
FIG. 3 shows one embodiment of a block diagram of the ECG-assisted blood
pressure
monitoring device 05 with key components and connections. It should be
understood that a
typical device may include fewer or more components, connections and
configurations. The
conductive flexible ECG electrode pair comprises a ground electrode 55 and a
sensing electrode
50. The flexible electrode pair 50, 55 connects to the flexible electrode
amplification unit
(FEAU) 60. The flexible electrode amplification unit 60 is in close proximity
to the flexible
electrode pair 50, 55 - this combination constitutes the active flexible
electrode pair on the
cuff. Similarly, the rigid ECG electrode pair 20, 25 connects to the rigid
electrode amplification
unit (REAU) 65 - this combination constitutes the active rigid electrode pair
on the device box.
Both the active flexible electrode pair (50 and 55 along with 60) and the
active rigid electrode
pair (20 and 25 along with 65) connect to the electrical conditioning unit 70,
which has circuitry
for further amplification and filtering of the acquired ECG signal. The
bladder (not shown) inside
the blood pressure cuff 15 connects to the pressure control unit 80 through an
air hose 10. The
pressure control unit contains a motorized cuff inflation pump, pressure
transducer, and a
voltage-control pressure release valve (not shown). There are analog to
digital (A/D) and digital
to analog (D/A) converters between the CPU 85, the electrical conditioning
unit 70, and the
pressure control unit 80. Moreover, between the CPU 85 and the electrical
conditioning unit 70,
there is a band-pass filtering (BPF) unit 75 with frequency range 6-25 Hz.
Through the band-
pass filtering unit 75, the CPU 85 obtains precise and noise-free real-time
ECG R-peak
information for controlling cuff deflation. The CPU 85 runs software to
interact with these
modules (70, 75, and 80) to: (i) achieve cuff inflation and (ii) achieve a
controlled cuff deflation,
during which it acquires simultaneous ECG and oscillometric data. The CPU 85
also runs
software for analyzing the acquired ECG and arterial pulse wave data,
displaying relevant
information on the liquid crystal display 30, storing it in the memory 95, and
transmitting it
wirelessly to a personal computer/smartphone via the wireless hardware 90
using an antenna
35. The clock 100 attached to the CPU 85 ensures that all information is
synchronized and time
stamped.
FIG. 4 shows one embodiment of a circuit diagram of the flexible electrode
amplification
unit 60 for the flexible electrode pair 50, 55. It should be understood that a
typical device may
include fewer or more components, connections, and configurations. The
electrode pair
comprises one sensing flexible ECG electrode 50 and one ground flexible
electrode 55. The
combination of input resistor R1 and input capacitor C1, acts as a high-pass
filter. This high-pass
filter passes all frequencies above 0.1 Hz, thus removing low frequency
baseline drift from the
ECG signal. For ECG current amplification, a low power operational amplifier
(OPAMP) 105 is
used. The operational amplifier 105 grounding resistor R3 and the feedback
resistor R4 provide
an ECG voltage gain of (1 + R4/R3). For example, if R3 = 50 KK2 and R4 = 250
Kf2, then ECG voltage
gain is 6. The combination of operational amplifier 105 feedback resistor R4
and capacitor C4,
acts as a low-pass filter. This low-pass filter passes all frequencies less
than 100 Hz, thus
removing high frequency noise from the ECG signal. Therefore, in totality, the
flexible electrode
amplification unit 60 acts as a band-pass filter with frequency range 0.1-100
Hz. This frequency
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range is ideal for studying all useful features of an ECG signal. A Schottky
diode pair 110 is
connected as shown to protect the operational amplifier 105 from static
voltage overload and
saturation that may occur from the electrode pair side. That is, if VIN
exceeds a certain
predefined value (for example, if VIN > 250 mV), then, the Schottky diode pair
110 will act as a
short circuit to discharge current to ground. The capacitors C2 and C3 are
used for stabilizing the
power supply Vs to the operational amplifier 105. In this manner, the flexible
electrode
amplification unit 60, which is in close proximity with the associated
electrode pair 50, 55, helps
to remove static and other noise to provide good quality amplified output ECG
signal Vour. This
amplified ECG signal is then reliably transmitted with minimal transmission
loss and noise
interference for further amplification, filtering, and digitization. A similar
circuit (not shown) is
also used for amplifying the ECG signal from the active rigid electrode pair
20, 25.
FIGS. 5a through Sd show a six second section of the simultaneous ECG and
oscillometric
signals acquired by the ECG-assisted blood pressure monitor during cuff
deflation and their
analysis. FIGS 5e and 5f show the entire oscillometric and pulse transit time
envelopes derived
from these signals and the estimation of blood pressure from them. The pulse
transit time
envelope (FIG. 5e) in this case is calculated from ECG R-peak and maximum
slope of the arterial
pulse wave.
For the coefficient-based ECG-assisted oscillometric analysis, the first step
involves the
identification of ECG R-peaks, seen as the dots in FIG. Sa. This is followed
by superimposing the
temporal locations of the ECG R-peaks on the cuff pressure (CP) signal, the
dots in FIG. Sb. A
cuff pressure trend line is obtained (dotted line in FIG. Sb) using the ECG R-
peak information
and is used to de-trend the cuff pressure signal to obtain an oscillometric
(OSC) signal (solid line
in FIG. 5c). The ECG R-peak information is also used for finding peaks in the
oscillometric signal
(upper dots in FIG. 5c) - the maximum amplitude of the oscillometric signal
between every two
consecutive ECG R-peaks is determined. The oscillometric pulse peak
information is used for
finding troughs in the oscillometric signal (lower dots in FIG. 5c) - the
minimum amplitude of
the oscillometric signal between every two consecutive oscillometric pulse
peaks is determined.
The amplitudes of the oscillometric pulse troughs (lower dots in FIG. 5c) are
subtracted from
the amplitudes of the oscillometric pulse peaks (upper dots in FIG. 5c), and
corresponding cuff
pressures (solid line in FIG. 5b) are used to obtain the oscillometric
envelope (in FIG. 5e). The
maximum of the oscillometric envelope is used for evaluating mean pressure
while empirical
coefficients are used for evaluating diastolic pressure and systolic pressure
(MAP = 96 mmHg,
DP = 83 mmHg, SP = 118 mmHg in FIG. 5e).
The coefficient-based pulse transit time-cuff pressure analysis follows from
the coefficient-
based ECG-assisted oscillometric analysis. First, the oscillometric signal
(solid line in FIG. 5c) is
differentiated to obtain its derivative (solid line in FIG. 5d). Then the ECG
R-peak information
(dots in FIG. 5a) is used to find peaks in the derivative of the oscillometric
signal (dots in FIG.
Sd) - the maximum amplitude of the derivative of the oscillometric signal
between every two
consecutive ECG R-peaks is determined. Pulse transit time is measured in
milliseconds between
the ECG R-peaks (dots in FIG. 5a) and the peaks of the derivative of the
oscillometric signal
(dots in FIG. Sd), and corresponding cuff pressures (solid line in FIG. Sb)
are used to obtain the
pulse transit time envelope (in FIG. 5f). The maximum of the pulse transit
time envelope is used
for evaluating mean pressure while empirical coefficients are used for
evaluating diastolic
pressure and systolic pressure (MAP = 97 mmHg, DP = 85 mmHg, SP = 114 mmHg in
FIG. 5f).
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FIGS. 6a and 6b show a five second section of the simultaneous ECG and
oscillometric pulse
wave signals acquired by the ECG-assisted blood pressure monitor during cuff
deflation, and
their analysis. FIGS. 6c and 6d show the entire pulse transit time envelopes
derived from these
signals and the estimation of blood pressure from them.
5 Pulse transit time is measured in milliseconds between ECG R-peaks (dots in
FIG. 6a) and
oscillometric (OSC) pulse tops (squares in FIG. 6b), and corresponding cuff
pressures (not
shown) are used to obtain the maxima pulse transit time envelope (squares in
FIG. 6c). The
maximum of the maxima pulse transit time envelope is used for evaluating
systolic pressure (SP
= 103 mmHg in FIG. 6c).
10 Pulse transit time is measured in milliseconds between ECG R-peaks (dots in
FIG. 6a) and
oscillometric pulse bottoms (triangles in FIG. 6b), and corresponding cuff
pressures (not shown)
are used to obtain the minima pulse transit time envelope (triangles in FIG.
6d). The maximum
of the minima pulse transit time envelope is used for evaluating diastolic
pressure (DP = 68
mmHg in FIG. 6d).
FIG. 7 is a flowchart showing the sequence of steps involved in the operation
of the ECG-
assisted blood pressure monitor to estimate systolic, diastolic, and mean
blood pressure. The
analysis unit is divided into a number of subunits for performing different
analyses. When a
recording is initiated by pushing the start button at step 21, the device
applies alternating
current through the electrodes using step 155. Based on the applied
alternating current, step
160 checks whether the electrode contact is proper or not. In case the
electrode contact is not
proper, step 165 advises the user to refer to the user manual for
troubleshooting and for
reinitiating the measurement. If the electrode contact is proper, then step
170 inflates the cuff
to a pressure above the expected systolic pressure. This is followed by
initiation of cuff
deflation, which is controlled by step 175. During cuff deflation, the
analysis unit step 180
acquires simultaneous ECG and oscillometric pulse wave data through the
electrodes. The
quality of the incoming ECG and arterial pulse wave data is checked in real-
time by the analysis
unit in step 185. if incoming data quality is not satisfactory, step 165 again
advises the user to
refer to the user manual for troubleshooting and for reinitiating the
measurement. If incoming
data quality is satisfactory, then the ECG and arterial pulse wave data starts
getting stored in
the memory at step 95. At the same time, the analysis unit in step 190 starts
to detect ECG R-
peaks in real-time. Step 195 checks for ECG R-peak quality in real-time. If
ECG R-peak quality is
not good, then nothing happens (step 200) and the cuff deflation step 175
deflates the cuff
without assistance from R-peaks. If ECG R-peak quality is satisfactory, then
step 205 feeds ECG
R-peak information to the cuff deflation step 175, which is then controlled by
R-peaks. Once the
cuff is deflated below the expected diastolic pressure, the measurement is
complete.
In FIG. 7, that analysis unit at step 210 analyzes ECG data stored in memory
step 95 to
detect R-peaks. Step 215 checks the quality of R-peaks. If ECG R-peak quality
is not satisfactory,
then step 245 analyzes arterial pulses without assistance from R-peaks. At
step 250 th analysis
unit then creates an oscillometric (OSC) envelope and computes blood pressure
using empirical
coefficients. This information, which comprises systolic, diastolic, and mean
pressure, is then
presented to the user through the display step 31. Moreover, If ECG R-peak
quality is not
satisfactory and blood pressure is computed without ECG R-peak assistance, at
step 255 the
analysis unit generates an alarm to alert the user. The user can then push the
end button at
step 41 to stop the monitor.
CA 02776204 2012-05-02
11
In FIG. 7, if the analysis unit at step 215 determines the ECG R-peak quality
to be
satisfactory, then at step 220 analyzes arterial pulses with the assistance of
R-peaks. At tep 225
it creates an R-peak assisted oscillometric envelope to estimate blood
pressure using empirical
coefficients. At step 230 the analysis unit creates a pulse transit time (PTT)
envelope (by
measuring time between ECG R-peak and maximum slope of arterial pulse peak) to
estimate
blood pressure using empirical coefficients. At step 235 the analysis unit
creates two pulse
transit time envelopes (one by measuring time between ECG R-peak and top of
arterial pulse
peak and other by measuring time between ECG R-peak and bottom of arterial
pulse peak) to
estimate blood pressure without empirical coefficients. The information from
the three blood
pressure estimations at steps 225, 230, and 235 is then sent to the blood
pressure information
fusion at step 240, which optimizes and fuses this information to generate a
single estimate of
systolic, diastolic, and mean pressure. This information is then presented to
the user through
the display step 31. The user can then push the end button at step 41 to stop
the monitor.
The embodiments presented will allow users to acquire ECG signal during
regular, almost
unchanged, blood pressure monitoring routine. They also allow for an
alternative way of
estimating systolic and diastolic blood pressure, which is more robust
especially in cases of
obesity, arrhythmias and atrial fibrillation. In addition, vessel stiffness is
estimated. While above
description contains many specificities, these should not be construed as
limitations on the
scope of the invention, but rather as an exemplification of preferred
embodiments thereof.
Many other variations are possible. For example, the blood pressure monitor
can present other
physiological parameters extracted from the ECG signal, for example, heart
rate variability
metrics. The monitor can be used as a wearable blood pressure monitor where
ECG and blood
pressure can be acquired periodically for long-term blood pressure monitoring.
The blood
pressure monitor can be integrated with a smartphone in a way that it is
physically attached to
the smartphone and can be used as a single device in which case all the
processing will be done
directly on the smartphone.
Accordingly, the scope of the invention should be determined not by the
embodiments
illustrated, but by the appended claims and their legal equivalents.
